Some vehicles, such as a motorcycle, are provided with a friction clutch between a crankshaft of an engine and a transmission shaft of a transmission which is coupled to a wheel. The friction clutch is configured to cause a drive plate which is rotatable integrally with the crankshaft and a driven plate which is rotatable integrally with the transmission shaft to contact each other, thereby transmitting rotation of the crankshaft to the wheel via the transmission, and to cause the drive plate and the driven plate to be away from each other so as not to transmit the rotation.
In a deceleration state resulting from gear downshifting during driving, a torque generated in the wheel coupled to the transmission is transmitted to the engine via the friction clutch. This torque is named a back torque. The friction clutch is provided with a back torque reducing device to prevent the back torque from being transmitted to the engine or to reduce the back torque being transmitted.
For example, in a back torque reducing device disclosed in Japanese Laid-Open Patent Application Publication NO. 2006-64157, a clutch cam is disposed at an opposite side, with respect to a clutch hub, from a pressure plate. A pin for adjusting a moving range of the clutch cam extends from the pressure plate into a clutch outer part and is inserted into a hole provided in a clutch hub such that a tip end faces the clutch cam.
In the friction clutch including the back torque reducing device disclosed in the above patent document 1, it is not easy to mount the pressure plate to the transmission shaft. It is necessary to mount the pressure plate to the transmission shaft with the clutch hub attached, in such a way that the pressure plate is coaxial with the transmission shaft while inserting the pin into the hole of the clutch hub.
Since it is difficult to see the hole of the clutch hub which is covered with the pressure plate when mounting the pressure plate to the transmission shaft, it is difficult to insert the pin into the hole.
In a motorcycle in which the transmission shaft is typically provided to extend along a horizontal direction, it is necessary to adjust the position of the transmission shaft around the center axis and to align the position of the pin and the position of the hole while carrying the pressure plate correctly in the center axis direction of the transmission shaft. This makes it more difficult to mount the pressure plate to the transmission shaft.
Furthermore, in the above configuration, it is necessary to form in the pressure plate the hole into which the pin is inserted and to form in the clutch hub the hole into which the pin is inserted such that they are coaxial with high accuracy. Therefore, a demand for processing accuracy increases to a comparatively high level. As a result, it is difficult to improve productivity and to reduce manufacturing cost.
Accordingly, an object of the present invention is to provide a back torque reducing device of a friction clutch which can be easily assembled and can improve its productivity.